The mechanisms by which cells transform to alternative states of differentiation are being studied in a model system. In the insect Manduca sexta simple tubular epithelial glands function as silk glands in the caterpillar and salivary glands in the adult moth. A single uniform population of differentiated silk gland cells transform synchronously into four differentiated cell populations in the adult gland without cell division, death, or large scale morphogenetic movements. This system is being used to study the timing of adult cell determination and the process of cellular differentiation. The necessity for replication of DNA for either determination or adult differentiation is being assessed. BIBLIOGRAPHIC REFERENCES: R.S. Hakim (1975) When do lepidopteran silk glands become competent to transform to their adult roles? Midwest Regional Development Biology Conference, Proceedings, page 10, abstract. R.S. Hakim and F.C. Kafatos (1974) The structure and salivary function of the labial gland in adult Manduca sexta. Tissue and Cell 6, 729-750.